Level structures on cyclic covers of $\mathbb{P}^n$ and the homology of Fermat hypersurfaces

Eduard Looijenga

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arXiv · 2602.16599

Level structures on cyclic covers of $\mathbb{P}^n$ and the homology of Fermat hypersurfaces

Eduard Looijenga

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Abstract

Let $Z'\subset \mathbb{P}^{n}$ be a smooth projective hypersurface of degree $d>1$ and let $Z\to \mathbb{P}^n$ be the $\mu_d$-cover totally ramified along $Z'$. We relate full level $d$ structures on the primitive cohomology $Z'$ with full level $d$ structures on the primitive cohomology of $Z$. In the special case, $d=n=3$ this makes a marking of a smooth cubic surface determine a level $3$-structure on the associated cubic threefold, thereby answering a question by Beauville. We expect many more such applications.

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Eduard Looijenga. 2026-02-18. Level structures on cyclic covers of $\mathbb{P}^n$ and the homology of Fermat hypersurfaces. https://arxiv.org/abs/2602.16599

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